Typically, lamps used for general lighting utilize a tungsten filament that is heated to generate light. This process, however, is generally inefficient because a significant amount of energy is lost to the environment in the form of extraneous heat and non-visible, infrared and ultraviolet radiation. Other alternatives for general lighting include fluorescent lamps and light emitting diodes. While more efficient than incandescent lamps having tungsten filaments, fluorescent lamps tend not to have pleasing spectral characteristics, and light emitting diodes tend to be expensive.
It has been known for at least a century that electrons accelerated by high voltage in a vacuum, otherwise known as cathode rays, can cause compounds known as phosphors to emit light when the electrons strike those compounds. Much cathode ray tube (CRT) effort over the last century has been aimed towards apparatuses using tightly focused, deflectable electron beams for selectively exciting such phosphors for use in television, radar, sonar, computer, oscilloscope and other information displays; these devices are hereinafter referenced as data display CRTs. CRTs have not typically been used for general lighting purposes.
Data display CRTs typically have deflection circuitry for steering electron beams, and have such tightly focused electron beams that operation without deflection may “burn” their phosphor coating, causing permanent damage to the CRT. Such CRTs are often, but not always, operated by high voltage power supplies linked to their deflection circuitry.
Voltage multipliers driven by inverters have been used to provide the high voltage required to accelerate electrons in data display CRTs. For example, U.S. Pat. No. 5,331,255 describes a DC-to-DC converter having an inverter operating at about 1 MHz driving a Cockroft-Walton voltage multiplier to produce high voltage for driving a small data display CRT.
Electronic loads, such as compact fluorescent lamps, also tend to draw current spikes, primarily at voltage peaks of the incoming AC waveform. These current spikes cause the loads to have a poor “power factor,” which can cause inefficiency in a power system.
Devices that use a stream of electrons to excite a phosphor typically require at least one electron source. Thermionic cathodes are commonly used for generating an electron beam for use in CRTs, electron microscopes, x-ray tubes, and other applications. In common use in CRTs, the goals are usually high current, rapid modulation of the emitted beam, tight focus, and stable emission. The cathode is typically a component of an electron gun that emits, focuses, and modulates the emitted beam.